Hi
I am having trouble getting a stable baseline. Whenever I run the HPLC on just a monitoring status I get a cycling baseline noise that continues throughtout the monitoring process. I shutoff the pump (stopped flow) and continued to monitor the baseline. The noise sort of declined but the baseline continued to drift. I have attached a graph of the baseline noise.

[Note from Moderator: To download this file using Internet Explorer, right click on the file name. In the dialog box, select "Save Target As...". In the Save As box, change the file extension from "unk" to ".cdf" (for example, change "noise3646_cdf.unk" to "noise3646.cdf". Click Save.]

noise3646.cdf noise3646.cdf (5 k)

More iformation, please:

On-line mixing or premixed mobile phase?
If on-line mixing, high- or low-pressure?
Temperature-controlled or ambient?

Dear Sally:

Couldn't load your chrom. file.
A cycling baseline noise usually means that the pump pulse dampener has gone kaput. Check this up.

The main question tho', is which pump are you using: single piston or dual piston? With a dual piston, you can sometimes get away with a failed pulse dampener, if it has one. With a single piston pump, you can't. Whatever the manufacturer says, be it "free floating piston", or "rapid-refill technology" or whatever.

Not that single pistons are in any way inferior. They aren't but they are generally more prone to the kind of cycling noise you are getting, if their pulse dampeners fail.

This is the most likely cause of your cycling noise.

Hope you find this useful. Do let me know.

Rgds.

s.k. srinivas
stimulus/bangalore/india.

Hi I am using on-line mixing, with a pressure of
2800 psi and the temp is ambient. Although the room temperature did decrease during the day.

Sally,
Do you degass mobile phase?Is there restriction on the detector output?Look for source of air entering on low pressure side of pump.

OK, if you're using on-line mixing, the first thing to do would be to try using a pre-mixed mobile phase and see if the problem goes away. If it does, then look to the proportioning valve, mixer, etc. If it doesn't, then look for flow rate variations as suggested above.

-- Tom Jupille / LC Resources

Dear Sally:
Couldn't load your chrom. file, too.
Try to switch off the detector and to continue supervision on the screen of the monitor. If the drift baseline or noice will proceed, the reason in an electrical part of system means.

Advice on loading chromatogram files.

Unfortunately, Microsoft chose to use the same file extension (cdf) for "channel description files" that the AIA used for chromatography data files when they defined the interchange format. The result is that *Internet Explorer* tries to open the chromatograms, fails, and saves the file with the extension "unk". As far as I know there is no workaround for this. In order to view those chromatograms, you have to do the following:

1. Download the file by double-clicking on the link.
2. Use Windows explorer to rename the file from "xxxxxxx.unk" to "xxxxxxx.cdf".
3. Either use a view such as our Chrom Merge program or import the xxxxxxxx.cdf file into your data system.

If anyone is having problems, please feel free to e-mail me privately; I'll see what I can do to help.

-- Tom Jupille / LC Resources Inc.